Switch with axially spaced angularly offset rotary wiper contacts



March 1, 1966 S. GODEL ETAL.

SWITCH WITH AXIALLY SPACED, ANGULARLY OFFSET Filed Sept. 13. 1961 ROTARY WIPER CONTACTS 5 Sheets-Sheet l HQE SIEGFRIED Goes. By LESTER M|LLER,JR.

ATTORNEYS March 1, 1966 s, GODEL T 3,238,319

SWITCH WITH AXIALLY SPACED. ANGULARLY OFFSET ROTARY WIPER CONTACTS Filed Sept. 13, 1961 3 Sheets-Sheet 2 FIGS INVENTORS SIEGFRIED Gone;

y LESTER MILLERA A TTORNE YS March 1, 1966 s. GODEL ETAL 3,233,319

SWITCH WITH AXIALLY SPACED, ANGULARLY OFFSET ROTARY WIPER CONTACTS Filed Sept. 13, 1961 3 Sheets-Sheet 5 S P9 z/ 22 2; 24 2526 7 8 FIGS INVENTORS SIEGFRIED GooEL LESTER MILLERJJR.

ATTORNEYS United States Patent 3,238,319 SWITCH WITH AXIALLY SPACED ANGULARLY OFFSET ROTARY WIPER CONTACTS Siegfried Godel, Norwalk, and Lester Miller, Jr., Danbury, Conn., assignors to American Machine 8: Foundry Company, a corporation of New Jersey Filed Sept. 13, 1961, Ser. No. 137,909 9 Claims. (Cl. 200-11) through equal increments in either direction to successive positions in response to selective, intermittent energization of a pair of electro-magnets. Accordingly, among the objects of the invention is the provision of an improved contact assembly for a stepping switch, the contact assembly being compact, rugged, reliable, economical to manufacture and requiring low operating power.

Another object is to provide an improved rotary switch contact assembly which does not require any manual adjustments or alignments and in which the parts are placed automatically in their proper positions incident to assembly thereof.

Still another object is to provide an improved contact assembly having a plurality of movable contacts arranged so that they do not all simultaneously engage the fixed contacts associated therewith upon movement of the movable contacts into each successive position.

In order that the manner in which these and other objects are attained, in accordance with the invention, can be understood in detail, reference is had to the accompanying drawings, which form a part of this specification, and wherein:

FIG. 1 is an end elevational view of one embodiment of the invention;

FIG. 2 is a side elevational view, partly in longitudinal section, of the embodiment shown in FIG. 1;

FIG. 3 is a transverse sectional view through one bank of contacts of the device of FIG. 1;

FIG. 4 is a sectional view along line 4-4 of FIG. 3, but showing the upper end portion of the brush in elevation;

FIG. 5 is a top plan view, with parts in section, of the device of FIG. 1;

FIG. 6 is an exploded isometric view of portions of the embodiment shown in FIG. 1;

FIG. 7 is a top plan view illustrating another embodiment of a bank level of stationary contacts;

FIG. 8 is a vertical cross sectional view along line 88 of FIG. 7, and

FIG. 9 is a vertical cross sectional view along line 99 of FIG. 8.

Referring now to the drawings, the embodiment of the invention there shown includes a contact bank 10, a movable contact assembly 11, a ratchet wheel 12 for rotating contact assembly 11 and an indicator plate 13 for indicating the position of the movable contact assembly. Contact bank includes six bank levels fastened together by bolts 14 and nuts 15.

With reference to FIGS. 3 and 4, each bank level includes a support member 16, brush 17 and a plurality of fixed contacts arms 18-28.

Support member 16 is of moldable insulation material and is in the form of a relatively thin, fiat block having a straight edge 29 and an arcuate edge 30. Each support member also has a pair of pins 31 and a pair of recesses 32 arranged so that the pins of one support mem- 3,238,319 Patented Mar. 1, 1966 her fit into the recesses of the adjacent support member to align the bank levels. Further, each support member is provided with a pair of bores 33 through which bolts 14 extend.

As seen in FIG. 3, each fixed contact arm includes a body portion 34 which is embedded in its associated support member 16. Body portion 34 terminates at one end in terminal 35 which projects perpendicularly from edge 29. The terminals of all the fixed contact arms are of the same length, relatively stiff and parallel so that the switch can be plugged into a suitable socket. At its other end, each fixed contact arm has a contact tip 36 which extends from edge 30 along a radial path toward the center of curvature of edge 30.

Each of the fixed contact arms is of sheet metal and is fiat so that the fixed contact arms in each bank level lie in the same plane. The contact tips 36 in each bank level are evenly spaced along an arcuate path. Thus, bank 10 has a plurality of evenly spaced, parallel bank levels each having a plurality of coplanar fixed contact arms. The arcuate edges 30 of the bank levels form a semicylindrical surface from which the contact tips 36 project radially inwardly toward the axis of the semicylindrical surface.

Each brush 17 is composed of two halves, each of sheet metal and abutting the other except at their tip portions. The tip portions are bent as indicated at 38 in FIG. 3 to provide a pair of divergent, resilient tips 39 and 40. Each brush has a body 41 embedded in its associated support member 16 and a terminal 42 equal in length and parallel to terminals 35. Brush 17 and fixed contact arms 18 and 28 are each provided with a recess such as that indicated at 37 in FIG. 3, so that there is suflicient insulation around bolts 14 to prevent them from being electrically connected or shorted to any of the fixed contact arms and the brushes.

Movable contact assembly 11 comprises a shaft 43 provided with a pair of diametrically opposed permanent keys or splines 44. With reference to FIGS. 5 and 6, each spline has a straight portion 46 at one end and a spiral or helical portion 47 at its other end, portion 46 being parallel to the axis of shaft 43. Ratchet wheel 12 and indicator plate 13 have suitable keyways engaged with splines 44 so that rotation of ratchet wheel 12 positively rotates shaft 43 and the various parts mounted thereon. A washer 48 of insulation material is splined to shaft 43 and lies between ratchet wheel 12 and plate 13. Shaft 43 also has a flange 49 which abuts the ratchet wheel, an externally threaded end 50 and an axial bore 51 (FIG. 3) arranged so that shaft 43 can be mounted on an axle.

Shaft 43 is disposed so that its axis of rotation is coin cident with the axis of the cylindrical surface formed by arcuate edges 30 of support members 16. Thus, each bank level, including the fixed contacts therein, lies within a plane which extends transversely of the axis of rotation of the shaft, such plane being substantially perpendicular to the axis.

Associated with each bank level is a pair of wiper contacts 52 and 53. With reference to FIGS. 1 and 6, each wiper contact includes an arm 54 and an arm 55 which extend on opposite sides around an annular hub 56. Each of arms 54 and 55 is bent to form a tip 57 which lies spaced from the plane of the remainder of the contact, tips 57 of each contact being diametrically opposed. Further, each arm has a slot 58 which extends throughout a portion of a length of the arm and through tip 57 to increase the resiliency of the arm. Contact tips 57 can be -shaped as indicated at 57a in FIG. 2 to break with one contact prior to engaging the next contact, or it can be flattened as indicated at 57b to bridge adjacent contacts and make before break.

As will be clear from FIGS. 1, 3 and 6, arms 54 and 55 are generally V-shaped in plan, with the tip portions 57 located at the base of the V. Adjacent legs of the Vs of arms 54 and 55 join each other and hub 56, as shown, the arrangement being such that the tip portions 57 of each contact member are each spaced radially outwardly a substantial distance from the hub 56.

In each pair of wiper contacts, contacts 52 and 53 are arranged so that their adjacent tips 57 extend toward each other in directions axially of the shaft to successively engage fixed contact tips 36 therebetween. When there is no contact tip between the tips 57, the tips of contacts 52 and 5.3 engage each other.

Shaft 43 is of insulation material so that the movable contacts are electrically insulated from one another. A spacer washer 60 of conductive material is splined to shaft 43 and is disposed between each pair of contacts 52 and 53.. An oval-shaped wafer 61 of insulation material is splined to shaft 43 and is disposed adjacent to each contact 52 to prevent arcing between adjacent pairs of wiper contacts or between the wiper contacts and other components of the switch.

A washer 62 of insulation material is splined to shaft 43 and is disposed between each adjacent pair of wiper contacts and at either end of the movable contact assembly. A nut 63 is screwed onto the threaded end of shaft 43 so that ratchet wheel 12, washer 46, indicator plate 13, the wiper contacts, spacers, wafers and washers are clamped between nut 63 and end flange 49. The keyways and the bores in each of these elements are slightly larger than the corresponding dimensions of the shaft, so that the elements are free to shift under the compressive force due to tightening of nut 63 so that such compression force is balanced throughout the assembly.

In each pair of wiper contacts, contact 52 and contact 53 are disposed on opposite sides of the plane in which the fixed contact arms in the bank level associated therewith lie. The tips 39 and 40 of each brush continuously engage hubs 56 of the pair of contacts 52 and 53, respectively, associated therewith. The bend which forms such tips is closer to the axis of rotation than the location of tips 57 so that the wiper contacts freely pass by brushes 17. The resiliency in each tip generates sufiicient contact pressures between the tips of the brushes and the associated wiper cont-acts. Because the movable contacts and other elements on shaft 41 are free to shift axially, the pressures generated due to the bias of tips 39 and 40 shift the movable contacts to balance the pressures therebetween and thereby promote even wear throughout the contact assembly.

The keyways in each wiper contact are at the same predetermined position. Some of the wiper contacts are mounted with their keyways engaging the helical portions 47 of splines 44, so that, in the axial succession of wiper contacts, as seen in FIG. 2, the tip portions 57 are arranged in helical fashion in accordance with the helical configuration of splines 44. The angle of the helix is small and is sufiicient to prevent all of the tips 57 from simultaneously hitting the tips of the fixed contact arms upon movement into successive positions and to insure that, when in each position, each pair of wiper contacts engages a contact tip 36. Furthermore, the angle of splines 44 is sufficiently small to preclude any tendency for axial shifting of the parts due to the exertion of a frictional torque when the shaft is rotated.

In operation, the wiper contacts associated with each bank level are operative, upon rotation of shaft 43, to electrically connect the terminal of brush 17 successively to the terminals 35 of the fixed contact arms, the order in which such contact arms are engaged being determined by the direction of rotation of the shaft. Thus, in the position shown in FIG. 3, the wiper contact is operative to connect brush 17 to fixed contact arm 18. If the shaft 43 is rotated in a clockwise direction from the position shown in FIG. 3, brush 17 would be next connected to fixed contact arm 28, then to contact arm 27 and so on. If the shaft is rotated in a counterclockwise direction from the position shown in FIG. 3, then brush 17 is connected first to fixed contact arm 19, then to fixed contact arm 20, and so on. The teeth on ratchet wheel 12 are proportionally related in position and number to the fixed contacts so that the contact assembly can be actuated by a stepping motor of the type disclosed in the aforementioned copending application.

Although, in the arrangement shown in the drawings, the movable contact assembly is frictionally supported by the contact bank, it is to be understood that in actual practice booth are supported on. the switch frame in a manner similar to that disclosed in the aforementional copending application.

The embodiment of the stationary contact bank level illustrated in FIGS, 7-9 differs from that shown in the other figures by the manner in which the brushes and the pins and recesses are constructed. In FIGS. 7-9, those parts which are substantially identical to the corresponding arts of the first embodiment have like reference numerals.

In the embodiment shown in FIGS. 7-9, support member 16 has a pair of laterally spaced bores 65 in which a pair of pins 66 are press fitted part way so that the pins 66 of one bank level fit into the bores 65 of an adjacent ban-k level to align the bank levels. The exposed ends of pins 66 are of slightly reduced diameter to facilitate entry into the bores of the adjacent support member.

Brush 67 is of one-piece construction, as contrasted to being of two halves similar to brush 17, and has a tip portion split to provide a pair of resilient tips 69 and 70 which are bent and extend in opposite directions for engagement with adjacent wiper contacts. The edges of tip portion 68 which engage the tips 57 of the wiper contacts as they move into engagement therewith, are offset from being directly diametrically opposite the edges of the tip of contact 18, so that the tips 57 cannot simultaneously hit both contact 18 and brush 67 as they move into engagement therewith. To illustrate, edge 71 of contact 18 lies along a line 72 which passes through the center 73' of the axis of rotation of the wiper contacts, the line being spaced from edge 74 of tip portion 68 by a gap 75. Likewise, the opposite edge 76 of tip portion-68 is not directly diametrically opposed to the other edge of contact 18. Such construction is advantageous over arrangements of the type similar to the first embodiment because the maximum force necessary to rotate the wiper is less since the tips of the wiper contacts do not simultaneously hit any diametrically opposed edges.

Contact 28, which is adjacent to brush 67, has a beveled edge 77 substantially parallel to edge 76 and spaced therefrom a distance which allows a non-bridging tip 57a to bridge the gap as it moves between brush 67 and contact 28. This construction is obviously advantageous because it lessens the power requirements by eliminating the necessity of having to pry apart the tips 57a when they move between the brush and the adjacent contact. That is, since it requires less power to maintain the tips 57a apart than to pry them apart when once together, the power requirements of the second embodiment are less than in arrangements of the type of the first embodiment.

While only a single embodiment has been shown, it will be apparent that many changes can be made in the details and arrangement of parts without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

1. In a rotary stepping switch, the combination of a rotatable shaft; a fixedcontact ibank disposed adjacent to said shaft and comprising a plurality of sets of fixed contact elements, the contact elements of each of said sets bemg spaced apart in an arcuate series concentric with the axis of rotation of said shaft, each of said fixed contact elements including a portion projecting radially inwardly toward said shaft, said sets of fixed contact elements being spaced apart longitudinally of said shaft; a

plurality of wiper contacts spaced apart longitudinally of said shaft; mounting means mounting said wiper contacts on said shaft for rotation therewith to cause each of said wiper contacts to move into successive engagement with the fixed contact elements of a different one of said sets of fixed contact elements, said mounting means com-prising key means including a spiral spline maintaining said wiper contacts in predetermined relative angular positions such that said wiper contacts are precluded from simultaneously coming into contact with said fixed contact elements during movement into successive rotational positions but can simultaneously engage fixed contact elements of the respective ones of said sets of fixed contact elements when in said successive positions; and a ratchet wheel secured to said shaft whereby stepwise rotational movement can be imparted thereto.

2. In a rotary stepping switch, the combination of a rotatable shaft; a plurality of fixed contacts each having a contact tip; means supporting said fixed contacts adjacent said shaft with said tips spaced along an arcuate path concentric with the axis of rotation of said shaft,

said tips projecting generally radially inwardly toward said shaft; a wiper contact mounted on said shaft for rotation therewith and including a central portion, and a pair of tips opposed to each other diametrically across said shaft and each spaced radially outwardly from said central portion, said tips and central portion being electrically interconnected;

said fixed contacts being so arranged that said contact tips thereof are spaced in an arcuate series extending for less than 180, whereby only one of said wiper contact tips can engage a fixed contact at any stage of rotation of said shaft; and a brush having a portion disposed in said arcuate path,

said portion of said brush projecting generally radially inwardly toward said shaft and terminating in a tip engaging said wiper contact central portion, said portion of said brush being arranged in substantial diametric opposition to one of said fixed contact tips whereby, when said wiper contact occupies a given position with one of said Wiper contact tips fully engaged with said one fixed contact tip, the other of said wiper contact tips is engaged with said portion of said brush; rotation of said shaft in one direction causing the respective tips of said wiper contact to approach corresponding edges of said one fixed contact tip and said portion of said brush,

said corresponding edges being angularly offset from each other in said one direction of rotation whereby said wiper contact tips come into contact with said corresponding edges sequentially rather than simultaneously during rotation of said wiper contact into said given position. 3. In a rotary stepping switch, the combination of a rotatable shaft having a spiral spline extending generally longitudinally thereof; a plurality of wiper contacts each including a hub portion and a tip portion, said hub portions each having a keyway, said wiper contacts being spaced apart axially along said shaft and mounted thereon for rotation therewith, said spline being engaged in said keyway of the hub portion of each of said wiper contacts and said tip portions of said wiper contacts being angularly displaced from each other in spiral fashion by reason of the spiral form of said spline; a plurality of sets of fixed contacts disposed adjacent to said shaft with said sets spaced apart' axially relative to said shaft to coact each with a different one of said wiper contacts, each of said sets including a plurality of fixed contact elements each having a tip portion, said fixed contact elements of each set being arranged with their tip portions projecting at least generally radially inwardly toward said shaft and spaced apart in an arcuate path concentric with the axis of rotation of said shaft; and means whereby stepwise rotary movement can be imparted to said shaft to bring the tip portions of said wiper contacts each into successive engagement with the tip portions of the fixed contact elements of the corresponding set of fixed contact elements, the angularly displaced relation of said wiper contact tip portions being such that, though each step of rotation of said shaft can bring said wiper contact tip portions into engagement with respective ones of said fixed contact tip portions, said wiper contact tip portions are precluded from simultaneously coming into contact with said fixed contact tip portions.

4. In a rotary switch, the combination of a rotatable shaft including a flange provided at one end of the shaft and a spiral spline extending generally axially along the shaft; a fixed contact bank disposed adjacent to said shaft and comprising a plurality of sets of fixed contact elements each embedded in a flat body of insulating material, each of said fiat bodies of insulating material being disposed transversely of said shaft and having an arcuate edge from which the fixed contact elements of the corresponding set project radially inwardly toward said shaft, the portions of said fixed contact elements which project toward said shaft being spaced apart in an arcuate series concentric with the axis of rotation of said shaft, said flat bodies being secured together in side-by-side relation so that said fixed contact sets are arranged in a series progressing axially of said shaft; a plurality of wiper contacts mounted on said shaft for rotation therewith, each of said wiper contacts including a tip portion spaced radially outwardly from said shaft, said wiper contacts being spaced apart axially of said shaft with said tip portion of each Wiper contact coacting with the arcuate series of projecting portions presented by a different one of said sets of fixed contact elements, said wiper contacts each including a hub provided with a keyway to accommodate said spline; means on said shaft coacting with said flange to apply a clamping force to said hubs; and means Whereby rotary movement can be imparted to said shaft.

5. In a rotary stepping switch, the combination of a rotatable shaft; a fixed contact tbank disposed adjacent to said shaft and comprising a plurality of sets of fixed contact elements, the contact elements of each of said sets being spaced apart in an arcuate series concentric with said shaft, each of said fixed contact elements including a portion projecting radially inwardly toward said shaft, said sets of fixed contact elements being spaced apart longitudinally of said shaft; a plurality of wiper contacts each comprising a flat member of conductive material including an annular hub and a pair of arm portions each joined at its ends to said hub and each including an intermediate portion defining a wiper contact tip spaced outwardly from said hub, said Wiper contact tips being diametrically opposed across said hub and both being displaced from the plane of said hub in the same direction, said hub having an opening through which said shaft extends and said wiper contacts each being mounted on said shaft for rotation therewith with the plane of each of said hubs being transverse to said shaft and with the wiper contact tips of each of said wiper contacts lying normally in a common plane transverse to said shaft, the axial location of each of said wiper contacts on said shaft being such that rotation of said shaft causes the wiper contact tips of each of said wiper contacts to traverse the arcuate series of fixed contact elements of a different one of said fixed contact sets; means interengaged between said shaft and said hubs of said wiper contacts maintaining said wiper contacts in positions such that the wiper contact tips are angularly displaced from each other in spiral fashion whereby, though each step of rotation of said shaft can bring said wiper contact tips into engagement with respective ones of said fixed contact elements, said wiper contact tips are precluded from simultaneously coming into contact with said fixed contact elements; and means fixed to said shaft whereby stepwise rotary movement can be imparted thereto; each of said sets of fixed contact elements also including a brush contact element projecting radially inwardly toward said shaft and terminating in a tip engaged with said hub of the respective one of said wiper contacts.

6. A switch in accordance with claim and wherein each of said arm portions is provided with a slot extending lengthwise of the arm portion and through the wiper contact tip provided by the arm portion.

7. In a rotary switch, the combination of a plurality of fixed contact sets each comprising a flat body of electrical insulating material having an arcuate edge, and

a plurality of fixed contact elements each comprising a body portion embedded in said body of insulating material and a flat tip portion projecting from said arcuate edge, said tip portions being spaced apart in an arcuate series and lying in a common plane;

means securing said contact sets together with said flat bodies of insulating material in side-by-side relation to provide a fixed contact assembly in which all of the arcuate series of fixed contact tip portions are concentric with a common axis and the common planes of said tip portions are parallel and spaced apart in the direction of said axis;

a rotatable shaft disposed adjacent said fixed contact assembly and extending at right angles to said common planes and arranged with its axis of rotation coincident with said common axis;

said tip portions of said fixed contact elements all extending generally radially inwardly toward said shaft;

a plurality of wiper contacts each comprising a pair of fiat conductive members each having a hub and a contact tip spaced outwardly from said hub and displaced from the plane thereof, said hubs each having an opening,

said shaft extending through the openings of all of said hubs and said flat conductive members each being secured to said shaft for rotation therewith;

the fiat conductive members of each of said pairs being disposed in side-by-side relation with their contact tips displaced toward each other and in normal engagement with each other,

said wiper contacts being spaced apart axially along said shaft and so located that, upon rotation of said shaft, the normally engaged pairs of contact tips of each of said wiper contacts travel in a different one of said common planes so as to engage and be separated by the corresponding ones of said fixed contact tips; means fixed to said shaft whereby stepwise rotary movement can be imparted thereto; and means interengaged between said shaft and said hubs of said wiper contacts and maintaining said wiper contacts in positions such that the contact tips thereof are angularly displaced from each other in spiral fashion whereby, through each step of rotation of said shaft can bring said wiper contact tips into engagement with respective ones of the tip portions of said fixed contact elements, said wiper contact tips are precluded from simultaneously coming into contact with said fixed contact elements.

8. A rotary switch in accordance with claim 7 and wherein each of said fixed contact sets comprises a fixed brush having a body portion embedded in said body of insulating material, said brush also comprising a flat portion projecting from saidarcuate edge of said flat body toward said shaft and terminating in a tip slidably engaged with the hub of at least one of the corresponding pair of said fiat conductive members,

said flat portion of said brush lying in the same common plane as the fixed contact elements carried by said body of insulating material.

9. In a rotary switch, the combination of a rotatable shaft;

a plurality of wiper contacts carried by said shaft for rotation therewith, said wiper contacts being spaced apart axially of said shaft and each having a contact tip spaced radially from said shaft;

a plurality of fixed contact sets each comprising a plurality of fixed contact elements,

a brush, and

means supporting said fixed contact elements and brush adjacent said shaft,

each of said fixed contact elements including a flat tip portion,

the fixed contact elements of each of said sets being disposed with said flat tip portions lying in a common plane and spaced apart in an arcuate series concentric with the axis of rotation of said shaft,

said brushes each including a fiat portion and the brush of each of said fixed contact sets being disposed with its flat portion in the same common plane as the fiat tip portions of the fixed contact elements of that set;

the axial location of said wiper contacts on said shaft being such that each of said wiper contacts sweeps across the brush and said fiat contact tip portions of a different one of said fixed contact sets during rotation of said shaft,

each of said brushes having an edge spaced from the edge of the next adjacent one of said fixed contact tip portions by a distance sufiiciently small that the contact tip of the corresponding one of said wiper contacts will bridge between said brush and said next adjacent fixed contact tip portions; means interengaged between said shaft and said wiper contacts and maintaining the wiper contacts in positions such that said wiper contact tips are angularly displaced from each other in spiral fashion whereby, though each step of rotation of said shaft can bring said wiper contact tips into engagement with respective ones of said fixed contact elements, said wiper contact tips are precluded from simultaneously coming into contact with said fixed contact elements; and means fixed to said shaft whereby stepwise rotary movement can be imparted thereto.

References Cited by the Examiner UNITED STATES PATENTS 597,470 1/ 1898 Norden. 1,381,805 6/1921 Crewdson 28753 1,803,995 5/1931 Chilton 28-753 1,891,247 12/1932 Shapiro 200-14 2,186,949 1/1940 Allison et al 200-15 2,401,037 5/1946 Arvin 338132 2,522,715 9/1950 Graybill et al 200 2,861,148 11/1958 Scheffer et a1. 200-105 3,086,096 4/1963 McGee 200-11 FOREIGN PATENTS 620,216 5/ 1961 Canada. 318,605 2/ 1957 Switzerland.

KATHLEEN H. CLAFFY, Primary Examiner.

7 BERNARD A. GILHEANY, Examiner. 

1. IN A ROTARY STEPPING SWITCH, THE COMBINATION OF A ROTATABLE SHAFT; A FIXED CONTACT BAND DISPOSED ADJACENT TO SAID SHAFT AND COMPRISING A PLURALITY OF SETS OF FIXED CONTACT ELEMENTS, THE CONTACTS ELEMENTS OF EACH OF SAID SETS BEING SPACED APART IN AN ARCUATE SERIES CONCENTRIC WITH THE AXIS OF ROTATION OF SAID SHAFT, EACH OF SAID FIXED CONTACT ELEMENTS INCLUDING A PORTION PROJECTING RADIALLY INWARDLY TOWARD SAID SHAFT, SAID SETS OF FIXED CONTACT ELEMENTS BEING SPACED APART LONGITUDINALLY OF SAID SHAFT; A PLURALITY OF WIPER CONTACTS SPACED APART LONGITUDINALLY OF SAID SHAFT; MOUNTING MEANS MOUNTING SAID WIPER CONTACTS ON SAID SHAFT FOR ROTATION THEREWITH TO CAUSE WITH OF SAID WIPER CONTACTS TO MOVE INTO SUCCESSIVE ENGAGEMENT WITH FIXED CONTACT ELEMENTS OF A DIFFERENT ONE OF SAID SETS OF FIXED CONTACT ELEMENTS, SAID MOUNTING MEANS COMPRISING KEY MEANS INCLUDING A SPIRAL SPLINE MAINTAINING SAID WIPER CONTACTS IN PREDETERMINED RELATIVE ANGULAR POSITIONS SUCH THAT SAID WIPER CONTACTS ARE PRECLUDED FROM SIMULTANEOUSLY COMING INTO CONTACT WITH SAID FIXED CONTACT ELEMENTS DURING MOVEMENT INTO SUCCESSIVE ROTATIONAL POSITIONS BUT CAN SIMULTANEOUSLY ENGAGE FIXED CONTACT ELEMENTS OF THE RESPECTIVE ONES OF SAID SETS OF FIXED CONTACT ELEMENTS WHEN IN SAID SUCCESSIVE POSITIONS; AND A RATCHET WHEEL SECURED TO SAID SHAFT WHEREBY STEPWISE ROTATIONAL MOVEMENT CAN BE IMPARTED THERETO. 